[Comb] Missed optimization opportunity for multiply used boolean operations

[Hideto Ueno]

hw.module @Baz(in %cond : i2, in %value : i2, out o1: i2, out o2: i2) {
  %0 = comb.and bin %cond, %value : i2
  %1 = comb.and bin %0, %value : i2
  hw.output %0, %1: i2, i2
}

Current output (canonicalization + export-verilog):

// Generated by CIRCT unknown git version
module Baz(     // nya.mlir:1:1
  input  [1:0] cond,    // nya.mlir:1:19
               value,   // nya.mlir:1:34
  output [1:0] o1,      // nya.mlir:1:51
               o2       // nya.mlir:1:63
);

  wire [1:0] _GEN = cond & value;       // nya.mlir:2:8
  assign o1 = _GEN;     // nya.mlir:2:8, :4:3
  assign o2 = _GEN & value;     // nya.mlir:2:8, :3:8, :4:3
endmodule

o2 could be just _GEN because value is a duplication. This is currently not optimized because _GEN is not flattened into o2 since _GEN is multiply used.

[Will Dietz]

This looks to be fixed by 6903 -- are there other opportunities to address, or okay to close?